Desulfurization of liquid fuel via extraction with imidazole-containing deep eutectic solvent

The desulfurization of liquid fuels with deep eutectic solvent (DES) newly synthesized from inexpensive constituents of imidazole and tetrabutylammonium bromide salt was conducted via liquid-liquid extraction. The aim of the work is to lower the sulfur content of liquid fuels to below the environmental regulation using DES in a process with low energy requirement. A simulated fuel containing dibenzothiophene (DBT) and thiophene as representative refractory sulfur compounds and a commercial-grade diesel fuel were used for this work. Quantitative monitoring of sulfur compounds in the raffinate phase of the fuels was performed using high-performance liquid chromatography and energy-dispersive X-ray fluorescence techniques. The results of sulfur extraction showed that DBT and thiophene extraction efficiencies of 70% and 47%, respectively, could be achieved from the simulated fuel in a single run extraction. Similarly, 47% total sulfur removal from the commercial-grade diesel fuel was achieved with the solvent. The deep desulfurizations of the fuels were successfully achieved in four and five successive stages with the simulated fuel and the diesel fuel, respectively. The solvent was effectively regenerated after the extraction process with both fuels, thus allowing for its repetitive usage.